SBG6580 Bridge Mode

Last April, after doing some research, I decided that the SBG6580 was going to replace my modem and old pre-N router. Within the past month or so, we've had to reset it several times a day for both the wireless and wired. When the wireless does work, the range is horrible. Motorola is sending us a new one, but we've decided to go with an ASUS router.

My question is: Can I just run an ethernet cable from the SBG6580 to the new router? Or do I need to put it into bridge mode? If I do need to put it into bridge mode, how would I do it, and why would I need to?

Does anyone know why my SB6580 doesn't work in bridge mode? I enable Rg PassThrough and/or disable NAPT mode, reboot the modem, and I cannot connect to the internet. I have the SB6580 going to a Linksys WRT160n. Help